1. Field of the Invention
The present invention relates to a purge air flow passage structure for supplying purge air to a surface of a light receiving part of an optical probe such as a radiation thermometer. Specifically, the present invention relates to a purge air flow passage structure that can effectively collects dust in purge air flowing in an air flow passage, and separates the dust from the purge air.
2. Description of the Related Art
In the case of the operation of a gas turbine engine, combustion air compressed by a compressor is mixed with fuel, and the combustion air including the fuel is combusted by a combustor to produce combustion gas. The combustion gas causes a turbine to rotate, generating engine driving force, that is, output torque.
According to such a gas turbine engine, temperature at a gas turbine entrance is raised so that performance of the gas turbine can be improved. However, when a temperature at the gas turbine entrance becomes higher than the tolerable temperature for the turbine blade, the turbine blade is damaged. For this reason, in order to suppress temperature raise of the turbine blade, engine control is performed to control temperature, or cooling structure for the turbine blade is adopted.
In terms of safety and service life of the engine, it is very important to perform monitoring to maintain: the condition (1) that temperature of the turbine blade does not become higher than a specified value; and/or the condition (2) that the cooling structure for the turbine blade normally function in the case of adopting the structure. A radiation thermometer 20 as shown in FIG. 1 is used to measure surface temperature of a turbine rotor blade. As shown in FIG. 1, the probe 1 of the radiation thermometer 20 is disposed at the turbine case 3 of the gas turbine. In FIG. 1, the reference numeral 21 designates a turbine stator blade, 22 the turbine rotor blade, and 23 combustion gas.
When dust or the like attaches to the surface of a light receiving part (lens or window) of the radiation thermometer probe 1, the temperature measurement cannot be normally performed. In addition, since the radiation thermometer is disposed at the turbine case, and the surface of the light receiving part of the radiation thermometer is exposed to combustion gas having high temperature, there is a possibility that the light receiving part is damaged, and the radiation thermometer is deprived of the temperature measurement function. For this problem, the purge air flow is brought to the surface of the light receiving part so that the dust can be prevented from attaching to the surface of the light receiving part, and further, the light receiving part can be protected from high-temperature combustion gas.
Compressed air extracted from a compressor is used as the purge air, but the purge air itself contains dust. If the flow of the purge air containing dust is brought to the surface of the light receiving part, the surface of the light receiving part becomes tainted by the dust of the purge air. Accordingly, it is necessary to remove the dust from the purge air before purging (cleaning) the surface of the light receiving part by using the purge air.
FIG. 2 shows a conventional example of a purge air cooling structure that has a function of removing dust from the purge air. In FIG. 2, the structure is partially cut out for understanding. In this drawing, the reference numeral 1 designates the probe of a radiation thermometer, 2 a lens (light receiving part), and 15 a nozzle. As shown in FIG. 2, a space for an air flow passage for purge air 9 is formed between the probe 1 of the radiation thermometer and the nozzle 15. The purge air 9 is supplied from the upstream air flow passage (at the right side in FIG. 2), and passes through a separation space formed near the outer edge of the lens attaching part where the lens 2 is attached. Thereafter, the flow of the purge air 9 is brought to the surface of the lens 2 so that the surface of the lens 2 can be purged by the purge air flow, and then, the purge air that was used to purge the lens 2 flows out to the turbine side. Specifically, in the separation space 8, the dust is separated from the purge air 9 by the inertia, the purge air 9 separated from the dust flows out from a penetration hole 7 at the upstream part in the separation space 8, and dust 10 flows out from a penetration hole 6 at the downstream part in the separation space 8 together with the purge air 9. The technique of purging the surface of the light receiving part by the purge air is disclosed in Japanese Laid-Open Patent Publication No. 11-96865.
However, even when the above-described separation space is provided, an effect of separating the dust from the purge air is not adequate, and it is difficult to completely separate the dust from the purge air. Thus, there is still a problem that the dust attaching to the surface of the light receiving part hinders temperature measurement.